Author Topic: 200a picking up local radio?  (Read 551 times)

Offline chrisryanolsen

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200a picking up local radio?
« on: November 09, 2020, 05:58:04 PM »
Welp, I recently did an amp re-build and when I went to test it for the first time, I'm getting local radio coming through the speakers. Stronger when the vibrato is turned up (using the exterior pot and the thumbwheel trim pot on the board). If I turn up the vibrato to its fullest, the radio signal is *very* strong. But even at lowest volume and lowest vibrato, the radio signal is present coming through the internal speakers. I have not tried using the aux out to see if it still happens (I don't currently have an amp to use).

Anyone had anything like this? Did I install my grounds incorrectly perhaps? I read several times that to reduce hum you should find and eliminate any 'ground loops' and that the stock Wurlitzer ground scheme is not very good, but when I look to find exactly *how* to find and eliminate ground loops, the info is from electrical engineers and it's all jargon...

Thanks!

Offline OZDOC

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Re: 200a picking up local radio?
« Reply #1 on: November 09, 2020, 07:31:10 PM »
Did you take pictures of the wiring before you disassembled things?
Where have you made earth connections that were not present before you disassembled?
David
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Offline chrisryanolsen

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Re: 200a picking up local radio?
« Reply #2 on: November 09, 2020, 10:31:18 PM »
I did take quite a few pics of my dis-assembly, however, there is *definitely* the possibility of grounding issues or things plugged in where they shouldn't be! The amp was non functional before I started the re-build process, so I have no idea if things were plugged in where they should have been to begin with! Ha.

I'm going to go through the 200A schematic I have again and double-check to see, but I did notice some inconsistencies between where it says leads should be plugged in, and where they were when I got the piano. I'll make a diagram of them and take some pictures and maybe someone where can tell me if I have things in the wrong place!

I'm also very interested if anyone has any good videos or blogs/articles about how to practically find ground loops, and what to do about them, or if someone has a 'tried-and-true' ground schematic they prefer to the stock schematic!

Offline OZDOC

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Re: 200a picking up local radio?
« Reply #3 on: November 10, 2020, 06:15:56 PM »
Sounds like you're on the right track.
Examine the assembly of the amplifier to the chassis and all the wiring loom connection points.
Put a red mark on the schematic where you identify a path to ground and check whether that connection exists in the original schematic.
Make sure that the principal path to ground through the power supply is actually continuous.

Another thought is: Did you use shielded cable for the signal connections from the reeds to the amplifier?
Have you simply got a missing shield connection?

David
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Offline chrisryanolsen

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Re: 200a picking up local radio?
« Reply #4 on: November 11, 2020, 12:24:00 PM »
Thanks for the reply, I'll be doing a thorough examination today, but I checked and all the ground connections appear to be exactly where they are listed on the schematic (and where they are in accordance with other images I've been able to find online, though I know that isn't gospel.)

Good idea of checking all shield connections, I didn't replace any wiring at all when working on the amp, and some of it, especially shield leads were looking pretty...weary... One of the reasons I didn't replace any wiring is because I have had a heck of a time finding shielded cable (both 2 core like the leads coming from the volume pot, or single core + shield lead) that seems to match up with what was used in the Wurlitzer originally... But I might have to do some more work to track some down to replace some of the more worn out wiring.

There was a blog a while back by a man named Johnny Illdigger who had done some DIY mods to a 200A to reduce the noise, and he mentioned removing some of the grounds that were redundant (I believe he said "The wurlitzer is grounded in way too many places) but I'm having a hard time determining which grounds would be safe to remove to test. I certainly don't want to remove grounds and make anything un-safe, but if they are redundant, they might be contributing to the issue. He mentioned specifically: "The pickup is grounded through the preamp pcb screw, remove the redundant ones." Would that mean the two grounds on either side of the harp assembly chassis would be redundant?

Appreciate the replies and patience as I learn.

Offline agarcia

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Re: 200a picking up local radio?
« Reply #5 on: November 11, 2020, 11:09:09 PM »
Was this picking up local radio before the re-build? Or was it not working at all before the rebuild? Just trying to understand if it's always been present or if it was caused by a change that was made during rebuild. This sounds more like a shielding issue than a grounding issue to me. Grounding noise typically is a constant annoying hum, but getting local radio means something in your circuit acting like an antenna.

Offline OZDOC

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Re: 200a picking up local radio?
« Reply #6 on: November 12, 2020, 01:26:49 AM »
Yes, I'm leaning the same way as Agarcia. What I'm wondering is - are you particularly close to a radio transmitter? If you took the Wurli to another location well away from your house, is the problem still there? You may be chasing something which is not a particular fault of your keyboard. I'm assuming that you've never had a working Wurli in the location you're currently at? It would be good to prove that the problem exists within the unit before tearing your hair out trying to solve it.
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Offline chrisryanolsen

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Re: 200a picking up local radio?
« Reply #7 on: November 12, 2020, 11:28:40 AM »
Good thoughts, I have been wondering about taking it somewhere else for testing as well to be sure. I'm not certain of my proximity to active radio towers, though I do think there are a few in my neighborhood.

I have never had a working Wurlitzer in my current location, no. It was working when I got it about 15 years ago, and over time through use or misuse (gigging mostly, and moving it across the country a couple times), it eventually fell into disrepair and has just been a pretty thing in the corner of the room for years. So when I went to do some maintenance, I found it was no longer functioning at all, so I did the amp re-build, but like I said, no wiring done at all. EDIT: forgot to mention that when the 200A *was* working, I never noticed it picking up radio signal ever.

If, as agarcia suggested, it is a shielding issue and not a grounding issue, are there any fixes for that? Aside from replacing shielded wiring (which I am going to do once I source cable, I found some local leads)? I've read about some simple wire-mesh faraday cages, or maybe lining the lid with something to help block incoming signal interference?

Thanks all!
« Last Edit: November 12, 2020, 01:57:59 PM by chrisryanolsen »

Offline OZDOC

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Re: 200a picking up local radio?
« Reply #8 on: November 12, 2020, 05:43:04 PM »
This sort of issue is almost impossible to help someone with by remote control.
It's easy enough to make suggestions and encouraging comments, but it's never clear whether the solution would be self-evident if you could actually lay your hands on the instrument.
For example, have you remembered to put the aluminium shield back over the reed bars?
I would avoid going down the path of adding things to the instrument like shielding until you have it working the way you remember it.
It's highly likely that it is just a single shielding connection that has mechanically broken while you've been working (or one that has not been resoldered to the amp pcb).
There is a huge double spread picture of the insides of a Wurlitzer 200A (with aluminium shield removed) in Classic Keys: Keyboard Sounds That Launched Rock Music that could help you track down missing or unusual wiring.
See attached thumbnail of the picture.
David
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Offline chrisryanolsen

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Re: 200a picking up local radio?
« Reply #9 on: November 12, 2020, 07:13:53 PM »
Not a bad way to sell books... ;) Haha.

I agree fully, it's difficult with many of the issues discussed on these (or any) forum when you aren't there to see the instrument. I plan to really dig in and make sure all my connections are solid (and likely will be replacing some wiring in the process) before making any actual additions or changes to the instrument.

I'll report back when I've had an hour to go through my wiring with a fine-toothed comb and comparing with the schematics.

Offline chrisryanolsen

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Re: 200a picking up local radio?
« Reply #10 on: November 18, 2020, 12:01:59 AM »
NOTE: Important context: I'm a big dummy and was looking at the 'Early version' schematic to trace leads for my 'Late version' 200A. Nearly all of this can be dis-regarded. Skip to the end for my only real question, regarding the wiring of the 5-lug terminal strip.

Alright, so I started to dig deep and trace all the leads according to the schematic and I found some inconsistencies that I would love some input on.

If you look at the attached image 'schematic_differences' you'll see I've drawn in color how my amp looks, any leads that I left alone are the same as this schematic. Starting with the leads from the preamp:

1. Grey Jacket from Reed Bar Preamp, leads are correct coming from the preamp, but where the connect to the amp is different: shielded drain wire connects to [10] instead of [4]

2. Leads starting from [18] and [19] on the amp going to the preamp are not separate wires but another shielded wire and the shield drain wire is connected to the key-side lead of R5 on the preamp (could this be one of those redundant, or unnecessary ground connections?)

3. Grey Jacket from Volume Control - shield drain wire is correct at [14], but my red wire connects to [15] whereas the schematic shows the red wire going to the post *next* to [15], labeled only as AMP. Then from 15, the lead is jumped over to [9]*

*This is one of the larger discrepancies. The schematic says there should be a Green Jacket from Aux. Volume Control that connects to posts [9] and [10] on the amp board. My machine does not have this at all. The green jacketed wire from the Aux Volume pot goes right to the Aux Output jack. And the RED jacket wire that starts at [11] and [12] on the amp board goes to the Aux Volume Control pot, NOT the Aux output jack like the schematic says.

4. As you can see in the illustration: In the schematic, the ground wire mounted to the right of the board next to the transformer goes to post [21] on the board. However, if you zoom in on the board, the schematic is mislabeled. Post [22] next to the diode is actually the post labeled as [21], whereas [21] is lower and to the left, next to a resistor. My ground wire is connected to my board at post [21], near the resistor... but if I'm supposed to follower the *picture* of the schematic, I would actually plug in the ground to post [22]... OOF, I'm sorry that is so convoluted...


Okay, so that is all the discrepancies on the schematic of leads connected to the board. However... I also have a very concerning discrepancy when comparing my wiring to images online. I've attached another photo 'fuse_strip'

Looking at it now I'm not sure how I didn't see it when I was replacing the fuse with the new fuse holder, but the way this 5-lug terminal strip was wired to begin with (and I assure you, it has been wired this way for the entire time I have owned the instrument) - the fuse is just connected to...nothing... Looking at it now I don't know how I didn't notice it before, and now I'm not certain how to fix it. Which wire leads should be connected to which terminal lugs, etc.

Okay, with that I think I've finished NaNoWriMo early! Haha. Thanks for reading and again, thanks for any insights. If you think it would be beneficial, I can do a little video walk-through and trace all the wiring on my machine in a video and upload it to youtube for anyone to look at.
« Last Edit: November 24, 2020, 01:27:51 PM by chrisryanolsen »

Offline chrisryanolsen

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Re: 200a picking up local radio?
« Reply #11 on: November 24, 2020, 01:29:59 PM »
So, you can see in my last post that I updated, but it turns out my real problem was being a big dummy. I was reading the 'Early' schematic to trace leads/wiring for my 'Late' model 200A... When I found the correct schematic, all my wiring to the amp and pre-amp matched up perfectly, except for that 5-lug terminal strip next to the volume/vibrato pots. I'm still not sure which wires should be soldered to which lugs...